Optical anisotropy and light outcoupling in OLEDs

Organic Light Emitting Diodes consist of a stack of thin layers that have a high refractive index and may have anisotropic optical properties. The emission from such a planar structure depends on the layering of the OLED, the anisotropy of the different materials and the orientation of the dipole emitters in the organic layer. OLEDs are used in lighting and display devices and the requirements for both applications are very different

Optical evidence for adsorption of charged inverse micelles in a Stern layer

Understanding the properties and behavior of nonpolar liquids containing surfactant and colloidal particles is essential for applications such as electrophoretic ink displays and liquid toner printing. Charged inverse micelles, formed from aggregated surfactant molecules, and their effect on the electrophoretic motion of colloidal particles have been investigated in quite some detail over the past years. However, the interactions of charged inverse micelles at the electrode interfaces are still not well understood. In some surfactant systems the charged inverse micelles bounce off the electrodes, while in other systems they are quickly adsorbed to the electrodes upon contact. In this work a fluorocarbon solvent doped with a fluorosurfactant is investigated in which the adsorption of charged inverse micelles to the electrode occurs slowly, leading to long-term charging phenomena. We propose a physical model and an equivalent electrical model based on adsorption and desorption of inverse micelles into a Stern layer with finite thickness. We compare two limiting cases of this model: the 'adsorption/desorption' limit and the 'Stern layer adsorption' limit. Both limits are compatible with electrical measurements. The 'Stern layer adsorption' limit additionally explains the optical measurements, because these measurements indicate that the diffuse double layer vanishes over time when a polarizing voltage step is applied. The obtained value for the Stern layer thickness and the proportionality between the charging time constant and the surfactant concentration are also compatible with the 'Stern layer adsorption' limit

Biopsychosocial rehabilitation in the working population with chronic low back pain:a concept analysis

OBJECTIVE: To identify the essential attributes of biopsychosocial rehabilitation for chronic low back pain in the working population.DESIGN: A concept analysis was conducted according to the 8-step method of Walker and Avant. This framework provides a clear concept and theoretical and operational definitions.METHODS: Five databases were searched, followed by a systematic screening. Subsequently, attributes, illustrative cases, antecedents, consequences and empirical referents were formulated.RESULTS: Of the 3793 studies identified, 42 unique references were included. Eleven attributes were identified: therapeutic exercise, psychological support, education, personalization, self-management, participation, follow-up, practice standard, goal-setting, social support, and dietary advice. Subsequently, illustrative cases were described. Antecedents, such as motivation, preparedness and a multidisciplinary team, were found, together with consequences such as decreased pain, less sick-leave and increased function and work status. Finally, examples of empirical referents were given.CONCLUSION: This study identified the attributes that are necessary to develop biopsychosocial rehabilitation intervention programmes for chronic low back pain. The defined concept of biopsychosocial rehabilitation for chronic low back pain may serve as a solid base to further develop and apply interventions. Future research should focus on the objectification of biopsychosocial rehabilitation and conceptualization regarding how personalization is done.</p

Tuning charge carrier transport and optical birefringence in liquid-crystalline thin films : a new design space for organic light-emitting diodes

B.L. acknowledges financial support from the Binational Science Foundation under grant No 2014396 and from the National Science Foundation under grant No 1639073. C.K. acknowledges funding from the Kent State University Internal Post-Doctoral Competition. M.C.K. acknowledges funding from the Belgian Agentschap voor innovatie door wetenschap en techniek under grant No IWT 131498.Liquid-crystalline organic semiconductors exhibit unique properties that make them highly interesting for organic optoelectronic applications. Their optical and electrical anisotropies and the possibility to control the alignment of the liquid-crystalline semiconductor allow not only to optimize charge carrier transport, but to tune the optical property of organic thin-film devices as well. In this study, the molecular orientation in a liquid-crystalline semiconductor film is tuned by a novel blading process as well as by different annealing protocols. The altered alignment is verified by cross-polarized optical microscopy and spectroscopic ellipsometry. It is shown that a change in alignment of the liquid-crystalline semiconductor improves charge transport in single charge carrier devices profoundly. Comparing the current-voltage characteristics of single charge carrier devices with simulations shows an excellent agreement and from this an in-depth understanding of single charge carrier transport in two-terminal devices is obtained. Finally, p-i-n type organic light-emitting diodes (OLEDs) compatible with vacuum processing techniques used in state-of-the-art OLEDs are demonstrated employing liquid-crystalline host matrix in the emission layer.Publisher PDFPeer reviewe